The present invention relates to a magnetic tunnel junction device and a memory device including the magnetic tunnel junction device, and more particularly, to a magnetic tunnel junction device capable of storing multi-bit data in a limited area and a magneto-resistance memory device including the magnetic tunnel junction device.
A dynamic random access memory (DRAM), which is a widely used semiconductor memory device, has advantages of high operation speed and high integration. However, the DRAM is a volatile memory device that loses data when a power supply is cut off, and the DRAM performs a refresh operation to prevent any loss of stored data. Meanwhile, a flash memory is a non-volatile memory device and may be highly integrated, but the flash memory has an uncompetitive operation speed. As compared with the DRAM and the flash memory, a magneto-resistance random memory device (MRAM) may have non-volatility, high operation speed, and high integration (scalability).
The MRAM device is a non-volatile memory device where data is stored by magnetic storage elements having different resistances according to a magnetic field between ferromagnetic plates. The magnetic storage element is a component including two ferromagnetic plates separated by an insulating layer. If polarities of the two ferromagnetic plates are parallel (the same), a resistance of magnetic storage element is minimized. Conversely, if polarities of the two ferromagnetic plates are opposite, the resistance is maximized. The MRAM device stores data based on cell's resistance, which changes according to the magnetization polarity of the ferromagnetic plates in the magnetic storage element. As a magnetic storage element, a Magnetic Tunnel Junction (MTJ element) may be used.
In the MRAM, the MTJ element may include a stacked structure of a ferromagnetic layer, an insulating layer, and another ferromagnetic layer. When electrons passing through a first ferromagnetic layer penetrate into an insulating layer serving as a tunneling barrier, the probability of an electron penetrating into the insulating layer is determined by the magnetic direction of second ferromagnetic layer. If two ferromagnetic layers have the same polarity (parallel magnetic direction), an amount of current tunneling into the insulating layer is maximized. Conversely, if two ferromagnetic layers have an opposite magnetic direction, an amount of current is minimized. For example, when a resistance recognized in response to the tunneling current is high, information stored in the MTJ element may have a logic level “1” (or “0”). If the resistance is low, information stored may have a logic level “0” (or “1”). In the MTJ, a first ferromagnetic layer is called a pinned layer because its polarity is set to particular value, and a second ferromagnetic layer is called a free layer because its polarity may be changed according to a magnetic field or a supplied current.